1. FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for detecting biological activity. More particularly, the present invention relates to a method for making rapid analysis of materials in which the presence of microorganisms or the like is suspected by infrared analysis of the head space of a container holding a growth medium which may be metabolized to provide a gaseous product.
When, for example, bacteria are cultured in a suitable medium including a carbon source, such as glucose, the carbon source is broken down to form CO.sub.2 during the growth and metabolism of the bacteria. It would be desirable to provide a direct non-invasive method for the analysis of the gaseous atmosphere produced over the growth medium in the head space in order to determine the presence or absence of biological activity.
2. Description of the Prior Art
Techniques have been developed for detection of bacteria which involve incubating a sample of material to be tested in a closed container with a radioisotope-labeled culture medium and monitoring the atmosphere produced in the container to determine whether or not radioactive gases are produced. A system of this type is disclosed in U.S. Pat. Nos. 3,676,679 and 3,935,073. Such systems are rapid and reliable but they have a number of disadvantages. Radioactive labeled materials are expensive and require special handling during storage, use and disposal. Moreover, such systems generally require the invasion of the head space above the growth medium to remove a sample of the gas produced by the microorganism to a separate sampling and detection chamber. However, the use of radioactive isotopes and instrumental systems has generally been considered necessary in order to detect the minute quantities of metabolic product gases produced in a relatively short period of time so as to detect the presence of biologically active species.
U.S. Pat. No. 4,182,656 describes a further method for detecting the presence of biologically active agents, such as bacteria, by monitoring the metabolic products of the biologically active agent in the head space of a container of a growth medium and the biologically active agent. In this method, a sample of material to be tested for the presence of biologically active agents is introduced into a sealable container partially filled with a culture medium comprising a .sup.13 C- labeled substrate which may be metabolized by the biologically active agent. The remainder of the container is filled with a culture gas. The container and its contents are subjected to conditions conducive to biological activity for a predetermined period sufficient for metabolism of the medium to produce carbon dioxide. Thereafter, the ratio of .sup.13 CO.sub.2 to .sup.12 CO.sub.2 in the culture gas in the container is determined and compared to the initial ratio of .sup.13 CO.sub.2 to .sup.12 CO.sub.2 in the culture gas in order to detect any differences which would indicate the presence of biologically active agents in the sample. This method also requires invasion of the head space in the container to remove a sample for the comparison testing.
There exists a need for a practicable, non-radioactive system for measuring metabolically produced gases without invasion of the container to remove a sample of the head space gas in order to detect bacteria and the like.
Accordingly, it is a principal object of the present invention to provide a rapid method for detecting the presence or absence of biologically active agents in a substance contaminated with the biologically active agent.
Another object of the invention is to provide a method for detecting the presence or absence of biologically active agents which uses comparatively inexpensive apparatus and materials.
It is a further object of the present invention to provide an instrumental method for detecting the presence or absence of biologically active agents which does not require the removal of a sample of the head space gas from a container containing a fermented sample and a growth medium.
Another object of the present invention is to provide an instrumental system for detecting the presence or absence of biologically active agents which does not require the use of radioactive materials.
Further objects of the invention will become apparent from a consideration of the following description and the appended claims.